You can change the color of text to one that coordinates with your presentation’s theme, or you can choose any color. You can also fill text with gradients or images.
Go to the Keynote app on your Mac.
Open a presentation, then select the text you want to change.
To change all of the text in a text box or table cell, select the text box or table cell.
In the Format 
sidebar, click the Text tab, then click the Style button near the top of the sidebar.
Choose one of the following:
A color that coordinates with your theme: Click the pop-up menu below the Font section, then choose Text Color. Click the color well, then choose a color.
Any color: Click the pop-up menu below the Font section, then choose Text Color. Click the color wheel, then choose a color from one of the color palettes.
A two-color gradient fill: Click the pop-up menu below the Font section and choose Gradient Fill. Choose two colors. The color well shows colors that match the theme; the color wheel opens the Colors window, where you can choose any color. Use the controls to change the angle and direction of the gradient.
A custom gradient: Click the pop-up menu below the Font section and choose Advanced Gradient Fill. Click the color stops below the slider to choose colors. Click near the bottom edge of the slider to add another color stop. You can drag the color stops and use the other controls to change the blend, angle, and direction of the gradient.
To apply the gradient based on the length of the shape or text box (not the size of the selected text), select the checkbox next to “Apply gradient to entire object.” The gradient changes when the size of the object or text box changes.
Go to the Keynote app on your Mac.
Open a presentation, then select the text you want to change.
To change all of the text in a text box or table cell, select the text box or table cell.
In the Format sidebar, click the Text tab, then click the Style button near the top of the sidebar.
Click the pop-up menu below the Font section and choose Image fill, or choose Advanced Image Fill if you want to add a tint to the image.
Click Choose, navigate to your photos, then double-click an image with a .jpg, .png, or .gif filename extension.
If you chose Advanced Image Fill, click the color well (to the right of the Choose button) and select a tint color.
To make the tint more or less transparent, click the color wheel, then drag the Opacity slider.
If the image doesn’t look the way you expected or you want to change how the image fills the text, click the pop-up menu above the Choose button, then choose an option:
Original Size: Places the image inside the text without altering its original dimensions. To resize the image, drag the Scale slider.
Stretch: Resizes the image to fit the text’s dimensions, which might change the image’s proportions.
Tile: Repeats the image inside the text. To resize the image, drag the Scale slider.
Scale to Fill: Makes the image larger or smaller to leave no space in the text.
Scale to Fit: Resizes the image to fit the text’s dimensions, but maintains the image’s proportions.
To change the text color used by a reviewer for markup, see Add and print comments in Keynote on Mac.
Tip: You can set a keyboard shortcut to quickly change text to a specific color.